This invention relates generally to traffic responsive control systems for automatic sliding doors. More particularly, the present invention relates to sliding door sensors which sense traffic approaching the doorway and/or traffic present in the vicinity of the door threshold and produce signals for controlling the operation of automatic sliding doors so that the doors remain in an open position until the traffic clears the door threshold.
Conventional automatic sliding door systems are automatically operable in response to various sensor configurations for initiating an opening sequence or in response to commands from operation initiating devices such as a push plate, a card reader or a mat. For sliding door applications, three separate sensor units are commonly employed. Two approach sensors are positioned for coverage at each side of the sliding door, and a threshold or safety sensor covers the threshold area in which the moving door panels travel. The approach sensors are conventionally microwave field distortion devices or passive infra-red motion sensing devices. The threshold sensors are conventionally presence sensing devices such as infra-red through-beams.
In U.S. Pat. No. 4,823,010 assigned to the assignee of the present invention, a diffuse-reflective infra-red threshold sensor generates a detection zone that extends on both sides of the door threshold. The infra-red transmitters are pulsed in a time spaced sequence. The threshold sensor operation is coordinated with the operate or door opening signals from the approach motion sensors. A latch sets a relay for maintaining the doors in an open position when traffic is detected in the sensor detection zone. In a disclosed sensor, four infra-red transmitters and a photodiode are mounted in a module which is mounted generally above the threshold of the sliding door.
Installations which employ separate approach sensors and threshold or safety sensors are prone to a number of problems which may eventually result in improper sensor operation. Approach sensors which require replacement due to failure or uncompensatable drift may be replaced with a sensor model which does not have specifications compatible with the original equipment. In addition, the conventional multiple sensor configurations for automatic door systems present problematic installation requirements, require a relatively sophisticated sensor coordination and frequently present a cluttered appearence at the door header.
There are a number of general constraints that are applicable to all sensor systems which employ infra-red (IR) detection. For example, it is desirable to adjust a threshold presence sensor as frequently as possible for the existing background to compensate for changes in the level of reflected light from the floor and the position of fixed objects in the vicinity of the door. It is also desirable to update the background compensation periodically and to compensate for changes in the general environment of the sensor. For certain highly reflective environments, "dark" targets traversing the doorway such as shopping carts or individuals wearing dark colored clothing may actually reduce, as opposed to increase, the amount of reflected radiation which impinges the sensor. The detection of both bright and dark targets is especially desirable in the threshold zone. Both presence and directional motion detection are advantageous for approach zone detection functions. Detection of directional motion allows for signal processing which enhances the possibility of achieving a minimum hold open time for the door while also satisfying safety, convenience and reliability requirements, thereby resulting in significant energy savings.